In the prior art, when there are multiple load modules (a load module may be an electronic device, or may be a circuit) in a device, a power supply bus circuit needs to be used, and the power supply bus circuit includes a direct current to direct current (DC-DC) conversion circuit and a voltage adjustment circuit that are successively connected. The DC-DC conversion circuit provides a direct current signal of a steady voltage; and then, the voltage adjustment circuit performs voltage adjustment according to different voltages required by different load modules. It may be seen that a premise to ensure a steady electric signal provided by the voltage adjustment circuit is that the DC-DC conversion circuit outputs a constant direct current signal.
As shown in FIG. 1, a direct current ranging from 36 volts to 72 volts is adjusted to a direct current signal of a constant voltage by using the DC-DC conversion circuit, and the direct current signal of the constant voltage is used to supply power to each load module. When voltage transformation is performed on a direct current signal ranging from 36 volts to 72 volts, a duty cycle of a pulse width modulation (PWM) signal used to control both the twenty-third N-type metal-oxide-semiconductor (NMOS) transistor Q23 and the twenty-fifth NMOS transistor Q25 needs to be adjusted in real time, and a duty cycle of a PWM signal used to control both the twenty-fourth NMOS transistor Q24 and the twenty-sixth NMOS transistor Q26 also needs to be adjusted in real time. In addition, it is necessary to ensure that a PWM signal used to control the twenty-third NMOS transistor Q23, a PWM signal used to control the twenty-fourth NMOS transistor Q24, a PWM signal used to control the twenty-fifth NMOS transistor Q25, a PWM signal used to control the twenty-sixth NMOS transistor Q26, a PWM signal used to control a twenty-seventh NMOS transistor Q27, and a PWM signal used to control a twenty-eighth NMOS transistor Q28 are of a same cycle and same timing. Only in this way can it be ensured that the duty cycle of the PWM signal used to control the twenty-third NMOS transistor Q23 and the twenty-fifth NMOS transistor Q25 is adjusted, and at the same time, the duty cycle of the PWM signal used to control the twenty-fourth NMOS transistor Q24 and the twenty-sixth NMOS transistor Q26 is adjusted, so that power input from a primary coil of a transformer T3 is constant; and therefore, it is ensured that the DC-DC conversion circuit provided in FIG. 1 can output a direct current of a steady voltage.
Because a voltage range of the direct current signal input to the DC-DC conversion circuit is 36 volts to 72 volts, in order to achieve compatibility with the entire voltage range and meet an isolation requirement, it is extremely difficult to perform product selection and matching on electronic parts (including the PWM signals of the twenty-fourth NMOS transistor Q24, the twenty-sixth NMOS transistor Q26, and the twenty-third NMOS transistor Q23, the twenty-fourth NMOS transistor Q24, the twenty-fifth NMOS transistor Q25, the twenty-sixth NMOS transistor Q26, the twenty-seventh NMOS transistor Q27, the twenty-eighth NMOS transistor Q28, the transformer T3, and an inductor capacitor (LC) part), which results in a relatively high design cost; and in addition, electric signal conversion efficiency has to be sacrificed.
A worse disadvantage of the DC-DC conversion circuit shown in FIG. 1 is that in general circumstances, it is extremely difficult to ensure that a PWM signal used to control the twenty-third NMOS transistor Q23, a PWM signal used to control the twenty-fourth NMOS transistor Q24, a PWM signal used to control the twenty-fifth NMOS transistor Q25, a PWM signal used to control the twenty-sixth NMOS transistor Q26, a PWM signal used to control the twenty-seventh NMOS transistor Q27, and a PWM signal used to control the twenty-eighth NMOS transistor Q28 are time varying and of a same cycle and same timing, and therefore, it cannot be ensured that a voltage of a direct current output by the DC-DC conversion circuit is steady; and further, it cannot be ensured that a voltage of an electric signal provided by the voltage adjustment circuit for the load modules is constant.